Like a woman's skirt: "long enough to cover the subject yet short enough to make it interesting."

Please define "sex". Are you referring to intercourse or the whole act of fooling around, making out, foreplay, and intercourse?

Sex meaning intercourse--many women report that if it lasts longer than about ten minutes they become sore, tired, and bored. If one or the other of you desire intercourse to last longer, better me thinks to take periodic breaks and fill the intermissions with more making out and foreplay

Sex meaning Necking, Petting, Foreplay and intercourse--as long as you want.
Anything less than about 15 minutes is generally considered a "Quickie".

That said, women unlike men require a considerable warm up period. Plan to devote no less than half an hour to a good make out session before getting to the foreplay.

> What other things can be done in sex apart from just up,down,up,down.

UP / down is also in and out.

How about round and round?

Go to the SI101 Home page and click on the button that takes you to positions. Generally, the Woman Superior position is considered best for first timers because it places the woman in charge. She knows where the penis is, where her vaginal opening is, and can deftly bring the two together, saving the guy some possible embarrassment. In addition, she can position the tip where she wants, particularly if there is an intact hymen. Then she can apply just the right amount of pressure. Lastly, she can go as fast or as slow as desired and as shallow or as deep as she wants.

Begin learning more by reading the many informative articles in the Index found at the top of the forum's main page.

for the guys, the first time usually doesn't last very long at all. It is not uncommon for us to take an hour or so at times. That is with plenty of different types of play. Everything from light stroking, fingering and playing around, oral on each other, some intercourse, more oral, different position for intercourse, and then back to something else. Othertimes we take 10 minutes if we don't have alot of time and we can both enjoy that. Yes the long sessions are better, but the quickies are nice and definately better than nothing. I would think the first time will only last between 10-15 minutes. Just because of the newness and for the girl, she can get very sore quickly with just a small amount of penetration. Anything else after that is not pleasurable at all.

P.S.
As a post script to the above, do you know if your girlfriend masturbates and has orgasms? It may very well be that she does not and cannot; although if she does and can, then help her to have an orgasm or two as she desires before you attempt penetration. If there is going to be any discomfort with that, any post coital stimulation for the purpose will usually be in vain.

The longest time I've actually been having just intercourse was 45 minutes, and it was too long. 30 minutes of actual penetration is long, but okay I think.

I've had great sexual experiences lasting only 10 minutes. Quality, not quantity.

Please see the sticky post The Program on this website.
Longest? 4 hours.